This invention relates to drip-forming devices and methods for drip irrigation apparatus and to drip irrigation apparatus incorporating such devices and methods. Drip irrigation apparatus may be used for plants in the open air or under glass or under foil or film.
Drip irrigation apparatus in which water is supplied to discrete plants in drip-form has been used for some time to irrigate cultivation of various kinds, more particularly vines, citrus fruits, peaches, apples, olives and other fruits and also many vegetable and decorative plants grown under glass and foil. Drip irrigation is particularly useful in cases where the supply of water is limited since drip irrigation consumes much less water than other forms of irrigation. There are other reasons which make drip irrigation advantageous, such as the fact that the irrigation water can be enriched with nutrients. Drip irrigation has made it possible to have intense cultivation of light highly permeable soils which have little ability to store water. The very efficient use of water also reduces labor and costs as compared with the conventional overhead or spray irrigation system. The yields too are increased due to the reduced incidence of disease.
Basically, a drip irrigation system usually comprises a pumping facility and filter at the water source, e.g., a well or surface water, lines for water distribution and drip-forming devices to distribute the water over areas of ground. A wide variety of constructions are known but most have pressure-reducing means which produce such a considerable drop in the pressure of water at the exit orifice that the water can leave only in drip form. In simple systems the output of water decreases and the working pressure decreases and are therefore unsuitable for hillsides with varying gradients. For the water output to remain constant -- i.e., to remain unaffected by the working pressure -- so that the systems can be used more particularly for a varying gradient and different sizes of plant, it has previously been necessary to use pressure controllers which are of very complicated construction and therefore likely to go wrong and which are also very expensive.
According to the present invention, a drip-forming device for drip irrigation apparatus comprises a tube having a smooth internal surface and a smooth surfaced rod having one end inserted into the tube by an adjustable amount, the rod being formed with at least one longitudinal groove which extends along at least part of the length of the rod and which is in communication with the part of the interior of the tube not occupied by the rod and whose depth decreases progressively away from the said one end over at least part of the length of the groove. With such devices, the output of each device can be simply adjusted to suit the local requirements, irrespective of the size, alignment and supply pressure of the complete irrigation apparatus, by adjustment of the depth of insertion of the rod in the tube. For a constant pressure the water output decreases with increasing depth of rod insertion -- i.e., as the minimum cross-section of the groove at the point of insertion of the rod in the tube decreases. At different pressures depending, for example, on gradient, the water output from different devices can be made equal by varying the depth of insertion of the rods in the tubes appropriately, such depth being increased as the pressure increases - i.e., the minimum cross-section has to be decreased.
Preferably, the depth of the groove decreases continuously from the inserted end over at least part of the length of the groove thus permitting stepless adjustment of the output of the device. Preferably, the rod is engaged frictionally in the tube and its depth of insertion in the tube is capable of manual adjustment. While frictional engagement is preferred, other means of maintaining the rod position in the tube can be used, if desired.
The invention also includes, according to a further aspect, drip irrigation apparatus and method comprising a water delivery line and drip lines branching therefrom, each of the drip lines being terminated by a drip-forming device according to the first aspect of the invention. Preferably, the tube of each drip-forming device is constituted by the respective drip line.
The invention may be carried into practice in various ways but one preferred drip irrigation apparatus and the drip-forming devices thereof will now be described by way of example with reference to the accompanying drawings, in which: